The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known portable power tools typically have an electric motor received within a housing. One common type of electric motor used in power tools has a rotor, a stator, and brushes. The rotor includes a rotor shaft, laminations mounted on the rotor shaft, armature windings wound in slots in the lamination stack, and a commutator mounted on the rotor shaft and electrically connected to the armature windings. The stator may have field windings wound in laminations, or may have permanent magnets. The brushes are mounted in brush housings, often known as brush boxes, surrounding the commutator. Electric current is supplied from a power source through the brushes to the commutator and then to the armature windings.
The brushes and brush boxes are typically part of a brush assembly(ies). The brush boxes and brushes are disposed diametrically opposite to each other with the commutator disposed therebetween. The brush assembly(ies) includes springs that urge the brushes against the commutator.
FIG. 1 illustrates a half piece 102 of a conventional brush assembly 100. Each piece 102 in this design includes a base member 103 on which a brush box 104 is mounted. The base member 103 has a semi-annular periphery 106. Brush box 104 includes a mounting portion 116, an arm 118 connected to the mounting portion 116 and extending perpendicularly from the base member 103, and a metallic brush box 120. Brush box 104 receives a brush therein. The mounting portion 116 includes a plurality of legs 122 for crimping to corresponding cutout portions 124 in the base member 103 to secure the mounting portion 116 to the base member 103. The spring 101 includes one end connected to the arm 118 and the other end having a contact portion 132. The contact portion 132 is disposed adjacent to the second open end 128 of the brush box 120. When the brush is received in the brush box 120, the contact portion 132 of the spring 101 contacts the brush and urges the brush radially inwardly against the motor commutator.
FIG. 2 depicts the conventional brush assembly 100 including two half pieces 102 inside a power tool. As can be shown in this figure, the brush half pieces 102 are inserted inside a groove 103 of the tool housing. The brush box 120 are arranged around the commutator 34 of the motor 14. Bosses 134 are used to mate the two housing halves together after assembling the half pieces 102 is complete.
The brush assembly 100 depicted herein is for a direct current (DC) cordless power tools. However, similar brush assemblies may be used in alternating current (AC) corded power tools. Further, also the brush box 120 depicted in FIG. 1 mounted on a brush card 102, similar brush boxes are mounted directly into the tool housing around the commutator.
The conventional brush assembly described herein has several disadvantages. First, brush box 120 includes a large amount of metal, which is both expensive and requires a great degree of accuracy in performing procedures such as stamping, bending and crimping the metal components. In addition, the gap between the brush box 120 and the brush is prone to collecting dust and debris over time. This increases the wear on the brush over time and may even cause the brush to jam inside the brush box. A jammed or “hung” brush results in the tool failing during runtime and may even damage the motor commutator. Moreover, since the brush box 120 encloses all four sides of the brush, it limits direct brush exposure to airflow. This can raise the brush box 102 temperature to fairly high levels, particularly in high power applications such as power tools, which can potentially damage the tool housing.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.